It seems there is a problem with the fuel consumption and fuel flow of the Duke.Normaly the higher you fly, the less your fuel consumption is.However in the Duke no matter what altitude you fly the fuel consumption is the same.Just have a look at the fuel flow gauge, it doesn't move when you climb.I try 2 flights of 500 mn, one at 25000 ft the other one at 6000 ft and I burn more or less the same amount of fuel.Is it just me or have you noticed it as well ?

It seems there is a problem with the fuel consumption and fuel flow of the Duke.Normaly the higher you fly, the less your fuel consumption is.However in the Duke no matter what altitude you fly the fuel consumption is the same.Just have a look at the fuel flow gauge, it doesn't move when you climb.I try 2 flights of 500 mn, one at 25000 ft the other one at 6000 ft and I burn more or less the same amount of fuel.Is it just me or have you noticed it as well ?

It does when you lean properly. Haven't got automixture turned on by mistake have you?

No I lean quiet a lot (The manual said you have to overlean compare to real life due to some FSX restriction)Anyhow I have turn on the pilot advise so I think I lean properly and when I'm not too sure I do the Ctrl X key when prompted.

Then check your realism settings in the sim match EXACTLY with the recommendations in the manual - see `Flying Guide` page 2 or page 7 for more detail.

Ok here are the figure,first my setting, appart from the g effect its exactly the same as the one proposed by realair.then I set the duke for normal cruise climb : 27.5 RPM and 35.5 pressureEverytime I wait for FSX to display that I haven't lean properly and then press the Ctrl + X hence I'm sure the aircraft is correctly leanedNow just look at fuel flow at the different altitude :3000ft 6000 ft10 000 ft15 000 ft20 000 ftNow I can go up to 23 000 ft and keep the 35.5 pressureAfter 23 000 ft the pressure drop and so does the fuel flow but only because I can't maintain the 35.5 pressureQuestion is is it just me or do you have the same issue ?

That's because it is a turbo charged engine. You should not have to lean very much if you are not over the critical altitude.

MSFS has always had a fuel-flow issue. A weakness in its design, is that fuel-flow and power are tied directly to each other, because it uses that method to inflict the power penalty, for improper mixture. You can see how weird this is, by intentionally delaying the leaning, and then watch as fuel-flow actually INCREASES when you lean, until it reaches optimum.. and then continued leaning will cause fuel-flow to decrease.That oddity aside.. test your TAS (true airspeed) per galllon, at different altitudes; which translates into your range (real fuel economy, not GPH). Remember, that if you find that you don't get greater range at higher altitudes, that you might be encountering a headwind... so be sure to clear ALL weather, before testing.Also remember at lower manifold pressure (like at cruise), the optimum mixture (ctrl+X), is actually too rich.. Don't use keystrokes.. lean as you go.. it's more realistic and more fun.My rule, is to treat the fuel-flow gauge like a CHT gauge. Just keep leaning to keep it peaked as you climb.. and then lean just bit to the lean side of peak for cruising.

That's because it is a turbo charged engine. You should not have to lean very much if you are not over the critical altitude.

That's true in the real world.. but the MSFS flight model acts as though the air and fuel are mixed (carb or injection), on the low-pressure end of the intake system. You have to lean for altitude, as though it's normally aspirated.

Normaly the higher you fly, the less your fuel consumption is.However in the Duke no matter what altitude you fly the fuel consumption is the same.Just have a look at the fuel flow gauge, it doesn't move when you climb.I try 2 flights of 500 mn, one at 25000 ft the other one at 6000 ft and I burn more or less the same amount of fuel.Is it just me or have you noticed it as well ?

Ok, this is interesting. I have a couple observations. I'm not an airplane guru like some people, but my understanding is that as you fly higher, fuel consumption does not necessarily decrease. Instead, you should see an increase in efficiency due to the thinner air at altitude permitting a higher speed at a given power setting. A quick look at the "Pilots Charts" included with the RealAir Beech Duke shows that this is the case.According to those charts (page 7-9), you will have the same fuel flow whether you are at 6000 or 24000 feet. The difference is that you will have a greater speed at 24000 feet, allowing the aircraft to travel further. Above 24000 feet, the fuel flow does drop off but from my experience, the aircraft would have to be fairly light to achieve this altitude.But you also mentioned that over a flight of 500 NM, the actual fuel consumption was about the same. This is because it took a lot more fuel to get to 24000 feet than it did to get to 6000. The benefit of altitude really shows over long flights. Page 10 of the "Pilots Charts" shows that at distances of 350-400 NM, there won't be a significant difference in total fuel consumption. At a distance of 500NM, we are probably talking about a 5% (or so) difference. With a fuel load of 202 gallons, we would expect to see a range of 890 NM at 6000 feet, and 960NM at 23000 feet, so even if you go the full distance, we are still talking about less than 10% difference in total consumption. If fuel economy/range is an issue, you can reduce power further to make the aircraft more efficient - the manual suggests 45% seems to gain more benefit from altitude that the settings you were using. There's lots of variables here, not the least of which is FSX's handling of fuel flow. The screenshots you provided seem to verify what the manual says to expect.- Martin

That's because it is a turbo charged engine. You should not have to lean very much if you are not over the critical altitude.

I agree with you Mr. Cessnaflyer. Most tubo systems will effectively overcome the thinner air at higher altitudes by giving the engine intake system compressed (denser) air. Therefore the requirement to lean at altitude is minimized with forced induction engines such as those on the Duke.

I usualy lean manualy, I just use the automatic lean in this demonstartion to be sure to have relevant figure (the computer will always lean the same way)With the Duke you have to lean a lot even at low altitude, it is written in the manual and you can hear the engine needs leaning.I'm not a real pilot but I notice, if you take the default learjet or the Digital aviation cheyenne for exemple, that your fuel flow will decrease dramatically as you climb.If I make a 500 nm flight in the cheyenne or in the learjet one at 6000 ft and the other one at 25 000 ft I'm pretty sure that fuel consumption will be like twice higher at 6000 ft than at 25 000 ftI don't know if the Duke simulate the right way the fuel consumption but actuallywith the Duke there is limited interest in climbing high as you will have more or less the same fuel consumption and operational range at low altitude or at high altitude which is something I found weird.

I agree with you Mr. Cessnaflyer. Most tubo systems will effectively overcome the thinner air at higher altitudes by giving the engine intake system compressed (denser) air. Therefore the requirement to lean at altitude is minimized with forced induction engines such as those on the Duke.

Again.. this is true in the real world, but not in the MSFS world. You still have to lean for altitude. It's kinda like some older, super-charged radials; where the carbs were on the low pressure side of the intake system. The fuel and air got "mixed" BEFORE the pressurization.

I'm not a real pilot but I notice, if you take the default learjet or the Digital aviation cheyenne for exemple, that your fuel flow will decrease dramatically as you climb.If I make a 500 nm flight in the cheyenne or in the learjet one at 6000 ft and the other one at 25 000 ft I'm pretty sure that fuel consumption will be like twice higher at 6000 ft than at 25 000 ft

This where the MSFS is somewhat realistic. Turbine engines are designed to be more efficient at high altutudes.

I don't know if the Duke simulate the right way the fuel consumption but actuallywith the Duke there is limited interest in climbing high as you will have more or less the same fuel consumption and operational range at low altitude or at high altitude which is something I found weird.

Your fuel-consumption by the hour doesn't get better at higher altitudes.. but your true airspeed does. On longer flights (unless there's a crippling headwind), it is advantageous, range-wise, to get up in the thin air.

I usualy lean manualy, I just use the automatic lean in this demonstartion to be sure to have relevant figure (the computer will always lean the same way)With the Duke you have to lean a lot even at low altitude, it is written in the manual and you can hear the engine needs leaning.I'm not a real pilot but I notice, if you take the default learjet or the Digital aviation cheyenne for exemple, that your fuel flow will decrease dramatically as you climb.If I make a 500 nm flight in the cheyenne or in the learjet one at 6000 ft and the other one at 25 000 ft I'm pretty sure that fuel consumption will be like twice higher at 6000 ft than at 25 000 ftI don't know if the Duke simulate the right way the fuel consumption but actuallywith the Duke there is limited interest in climbing high as you will have more or less the same fuel consumption and operational range at low altitude or at high altitude which is something I found weird.

Ah, now we understand. You have little knowledge of the piston-engined power plant in aviation. Comparing the Duke (turbocharged piston) to either the Lear (turbofan) or Cheyenne (turboprop) is actually like comparing apples to... applied mathematics..!A turbocharged piston engine is a very different animal from a turbine engine. Forced air induction is used by both, as the concept of mixing fuel with air then igniting is common to both, but there the similarities end... In a piston engine the manifold pressure (power) declines with increasing altitude, reducing the actual performance until the aircraft reaches an altitude where it can no longer climb. That is its ceiling. Piston engine designers added a turbocharger (and in many cases a supercharger or even BOTH) to maintain that manifold pressure to higher altitudes and to boost the available power. The effect is to mask the decline of manifold pressure until a higher critical altitude is achieved. LEANING a piston engine involves balancing the available fuel flow to the available air pressure, something that no longer changes until much higher altitudes with the addition of a turbocharger (except in the inaccurate modelling that is baseline FSX). In the REAL world, a turbocharger makes the engine run hot, hot, HOT, and it is often recognised that fuel flow needs to be increased to provide not required by a turbine engine so it may actually have to run richer than optimum to avoid setting the engines on fire. We get some of that with the fantastic modelling of the Duke - lean and watch the temperatures rise at high power settings. Fuel flow as set up may not be a simple function of efficiency, but actually a complex equation involving the need to `overfuel` to keep the cylinder head and piston cool. But the turbocharger masks the fuel flow change with increasing altitude, so you set the speed and the cooling to match the set manifold pressure and prop speed values and until the turbo runs out of `puff` you will see no change in fuel flow, but you should in EGT, CHT and the need for cooler doors and ducts to be opened.